About 80% of world trade goes by sea and without the constant traffic of cargo ships crisscrossing the globe, modern civilization would grind to a halt in no time. However, the global shipping industry accounts for 3% of all global greenhouse gas emissions, a figure projected to rise to at least 10% by 2030.

The shipping industry is committed to reducing these emissions as much as possible but there is an elephant-sized problem standing in the way. Shipping depends on heavy fuel oil and alternatives like green ammonia, hydrogen, and methanol fall short because these fuels are not available in sufficient quantities. Worse, the electricity that would be required to create enough green ammonia or hydrogen would exceed the total electricity production capacity of the world.

Equally daunting is the fact that some commercial ships – such as bulk carriers, oil tankers, container ships, and those used in offshore construction – require power sources that have high energy density and can sustain themselves over long ranges.

To overcome this, the consortium behind the NuProShip II project is looking at how to fit Gen IV small modular nuclear reactors to heavy commercial vessels. The project's demonstrator concept is based on a 120-m (394-ft) Vard 3 offshore subsea construction vessel, designed by Fincantieri subsidiary Vard.

The idea is to come up with a simple, safe, self-contained reactor that can either be installed in a new ship or retrofitted to existing craft without having to rip out the gubbins from the engine room.

Several reactor concepts were assessed for vessels of different sizes, though they share key characteristics. Chief among them is the use of tri-structural isotropic (TRISO) fuel, consisting of ceramic-coated uranium particles capable of withstanding temperatures above 1,600 °C (2,912 °F). Such pebble-bed reactors are inherently safe because the nuclear reaction is self-regulating and they lend themselves to passive cooling systems while putting out about 15 to 45 MW of thermal power per module using supercritical CO? Brayton cycle reactors.

The cooling system is most likely to be helium because alternatives like molten salt and sodium don't play well when they come into contact with water. Meanwhile, using water as a coolant was rejected both on the grounds of complexity and the tendency of the public to associate water reactors with accidents like Fukushima. However, larger vessels would use lead-cooled reactors and perhaps molten salt.